We propose to develop novel inhibitors of HIV entry that target the highly conserved N-trimer pocket region of HIV gp41. Inhibition of this essential component of HIV's fusion machinery prevents viral entry and the establishment of infection. Our inhibitory peptides are composed of D-amino acids (D-peptides), which are resistant to natural proteases and are predicted to survive in the body for much longer periods of time than traditional L-peptide inhibitors. We will use a combination of structure-based protein design and phage display screening to identify D-peptides with high affinity for the N-trimer and strong antiviral potency in HIV entry assays. We also propose to make multimeric D-peptides that bind to gp41 with greater affinity and antiviral potency. We will determine the high-resolution structures of these D-peptides in complex with their N- trimer target to determine the sources of their potency and to guide the design of improved D-peptides. Potent D-peptide entry inhibitors would be useful both as an additional therapeutic component of an antiretroviral cocktail and for prophylactic microbicide use. These studies will also likely have broad applicability for the development of other D-peptide viral entry inhibitors and for improving our knowledge of D-peptide design in general. PUBLIC HEALTH RELEVANCE: The development of potent protease-resistant D-peptide inhibitors of HIV entry will be useful for the treatment of infected patients (therapeutic agent), as well as the prevention of new infections (prophylactic agent). A better understanding of D-peptide design will stimulate future development of these hardy peptides for diverse applications in scientific research and medicine.